AbstractBACKGROUNDEnvironmental, economic and safety challenges motivate shift towards safer materials for food packaging. New bioactive packaging techniques, i.e. addition of essential plant oils (EOs), are gaining attention by creating barriers to protect products from spoilage. Analytical pyrolysis gas chromatography–mass spectrometry (Py‐GC‐MS) was used to fingerprint a bioactive polylactic acid (PLA) with polybutylene succinate (PBS) (950 g kg−1:50 g kg−1) film extruded with variable quantities (0, 20, 50 and 100 g kg−1) of Origanum vulgare EO.RESULTSMain PLA:PBS pyrolysis products were lactide enantiomers and monomer units from the major PLA fraction and succinic acid anhydride from the PBS fraction. Oregano EO pyrolysis released cymene, terpinene and thymol/carvacrol peaks as diagnostic peaks for EO. In fact, linear correlation coefficients better than 0.950R2 value (P < 0.001) were found between the chromatographic area of the diagnostic peaks and the amount of oregano EO in the bioplastic.CONCLUSIONThe pyrolytic behaviour of a bio‐based active package polymer including EO is studied in detail. Identified diagnostic compounds provide a tool to monitor the quantity of EO incorporated into the PLA:PBS polymeric matrix. Analytical pyrolysis is proposed as a rapid technique for the identification and quantification of additives within bio‐based plastic matrices. © 2015 Society of Chemical Industry